Broad band antenna



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V. (3.- SMITH, JR. ETAL BROAD BAND ANTENNA Filed Jan. 2'7, 1965INVENTORS VALOR C-SMITH ,J'R. JOHNQWATSON Q M W m ATTORNEYS Mass.

Filed .l'an. 27, 1965, Ser. No. 428,332 7 Claims. (Cl. 343830) Thepresent invention relates to broad band antennas and, more specifically,to monopole antennas of the very broad band type.

Numerous configurations of monopole structures have been evolved andused for broad band reception and transmission including conical segmentmonopole structures and disc cage antennas, as two of the more common.While such structures can be employed over broad frequency bands, theyrequire, particularly at the lower frequencies, sizable and costlyconstructions and they do not lend themselves, in several particulars,to substantially direct scaling techniques, especially in the higherfrequencies, including the microwave range. It is, accordingly, to thepurpose of providing a new and improved broad band monopole antenna thatshall not be subject to the above-mentioned disadvantages that thepresent invention is primarily directed; it being an object of theinvention to provide a novel, simplified, less costly and less sizablebroad band antenna of this character.

A further object is to provide a novel antenna of more general use, aswell.

Other and further objects will be made apparent hereafter and will bemore particularly delineated in the appended claims. In summary,however, the antenna of the invention contemplates a closed loop ofcritically oriented sections from which substantially parallel arrays orconductors of radically different dimensions extend in oppositedirections. Preferred constructional details are hereinafter set forth.

The invention will now be described in connection with the accompanyingdrawing, the single figure of which is an isometric of a preferredembodiment thereof.

A closed loop L is shown comprising a first horizontally orientedcentral straight section 1 bounded by upper and lower substantiallyparallel spaced segments 1' and 1", fed near their centers by the innerconductor 2 and the outer conductor 2' of a coaxial feed line, so as toeffect a shunt-type of feed for transmission or reception. At the endsof the central straight section 1 similar diverging acute-angle sectionsare provided at 3 and 3, terminating, in turn, in similar horizontalstraight sections 5 and 5'. Upper and lower arrays 4 and 4' ofsubstantially parallel conductors or radiators extend in oppositedirections from the upper and lower segments of the loop L, andsubstantially coplanar therewith, and with the conductors 7 of the array4 being of much greater length than the conductors 7 of the array 4 forpurposes later explained. The lower ends of conductors 7 of the array 4and the upper ends of conductors 7 of the array 4 are connected togetherby a rectangular conductive frame 9 that also closes off the left andright hand ends of the loop sections 5 and 5'. The conductors 7 and 7'preferably are horizontally spaced a distance similar to the width ofthe loop L, but in all cases a distance very small compared to thesmallest wave length to be used with the antenna so as, in effect, topresent the appearance of a relatively continuous conductive surface.

It has been found that remarkably good matching can I 3,324,476 PatentedJune 6, 1967 be attained over frequency bands of as much as five-toonefrequency ratio, consistent with, for example, omnidirectional radiationpattern of vertically polarized radiation, provided the closed loop Lhas substantially the geometry above described and is provided with asection 1 of horizontal length less than A; of the maximum wave lengthof the band, with the transition or matching loop segments 33' divergingat angles of the order of substantially degrees, and with the horizontallength of the terminal extensions 5 and 5' being considerably shorterthan the length of the section 1, say of the order of A: as long. Such,broad band and omni-directional results have been obtained, moreover,with the overall vertical length of the frame 9 approximately of themaximum wave length of the band, a horizontal length of frame 9approximately 0.085 of such wave length, and a horizontal length of thesection 1 approximately 0.01 of the maximum wave length. To attain thebroad band matching results consistent with omni-directional pattern,furthermore, it has been found that the conductors of the upper array 4should be much longer than those of the lower array 4; say, in the ratioof about 9 to 1, more or less. In the case of the vertical polarization,the conductors 7 and 7 of the arrays 4 and 4 should be substantiallyvertical and thus substantially orthogonal to the straight section '1.

When the planar antenna of the present invention is employed on aircraftor in other areas where streamlining is essential, it may be imbedded ina plastic tear-shaped housing 11.

It has been found that this type of slab or planar vertically polarizedmonopole gives substantially the same electrical performance as the muchmore costly, spaceconsuming conical monopoles and disc cage antennas ofthe prior art, and provides, also, the advantage of less obstruction toancillary radiation equipment, such as,

radars and the like. Variation from the rectangular frame shape and thesharp angular configuration of the loop L may, of course, be effectedwithout departing from the spirit and scope of the invention, providedthe'critical relative dimensions and orientation of the parts aresubstantially maintained as above-described.

What is claimed is:

1. A broad band substantially planar antenna having, in combination, aclosed loop of substantially parallel spaced segments comprising acentral straight section terminating at its ends in similar divergingsections that terminate, in turn, in similar straight sectionssubstantially parallel to the central section but of shorter length,feed means connected to opposite spaced segments of the central loopsection, and a pair of arrays of substantially parallel conductorsextending in opposite directions from the loop sections, one array beingof much shorter length than the other.

2. An antenna as claimed in claim 1 and in which the spacing between thesaid parallel conductors is small compared to the minimum wavelength tobe used with the antenna.

3. An antenna as claimed in claim 2 and in which the said conductorsextend substantially orthogonally from the said straight sections of theloop.

4. An antenna as claimed in claim 1 and in which the angles ofdivergence of the diverging sections of the loop are substantially 1-60degrees with respect to the'central straight section.

5. An antenna as claimed in claim 1 and in which the overall length ofthe arrays is of the order of 0.2 A/max,

7. An antenna as claimed in claim 6 and in which the planar antenna isimbedded in a streamlined plastic housing.

No references cited.

HERMAN KARL SAALBACH, Primary Examiner.

R. D. COHN, Assistant Examiner.

1. A BROAD BAND SUBSTANTIALLY PLANAR ANTENNA HAVING, IN COMBINATION, ACLOSED LOOP OF SUBSTANTIALLY PARALLEL SPACED SEGMENTS COMPRISING ACENTRAL STRAIGHT SECTION TERMINATING AT ITS ENDS IN SIMILAR DIVERGINGSECTIONS THAT TERMINATE, IN TURN, IN SIMILAR STRAIGHT SECTIONSSUBSTANTIALLY PARALLEL TO THE CENTRAL SECTION BUT OF SHORTER LENGTH,FEED MEANS CONNECTED TO OPPOSITE SPACED SEGMENTS OF THE CENTRAL LOOPSECTION, AND A PAIR OF ARRAYS OF SUBSTANTIALLY